As used herein, mineral slurries are fluid mixtures of ground ore with water, where the ground ore particle size is generally less than 200 microns. A number of different ore minerals may be represented in a slurry. Froth flotation is a highly versatile method for physically separating particles based on differences in the ability of air bubbles to selectively adhere to specific mineral surfaces in a mineral/water slurry. The particles with attached air bubbles are then carried to the surface and removed, while the particles that remain completely wetted stay in the liquid phase. Froth flotation can be adapted to a broad range of mineral separations, as it is possible to use chemical treatments to selectively alter mineral surfaces so that they have the necessary properties for the separation. A large proportion of the world's base metal production is processed through flotation cells.
The optimisation of the flotation process is often dependant on the mix of ore mineralogies presented to the process, and not just the grade of the economic metal. There are a number of techniques that may be used to measure the composition of mineral slurries to aid process control. For example, representative sampling of slurries may be performed, where the samples are relayed to a laboratory for analysis of elemental and mineral composition using standard off-line techniques. However this approach often involves unavoidable delays that render the sampled data un-usable for short term process control.
To compensate for the delay, on-line slurry analysers have been developed. Within the context of the present invention, the expression “on-line” is used to indicate that magnetic resonance signals are obtained from certain materials in the mineral slurry as it passes through a pipe or the like. As a result, signal processing is able to occur on site, in real-time. In contrast, off-line analyses require that a sample of the slurry material be taken away for analysis.
The use of magnetic resonance sensors for quantitative detection or characterisation of minerals has been demonstrated in the laboratory. More recently the development of apparatus employing principles of magnetic resonance for on-line quantitative mineral slurry measurements has been attempted. One problem associated with mineral slurry measurements is that a varying amount of mineral particles pass at a variable flow rate through any such sensing apparatus. As a result, the varying solid material loading and composition affects the stability of the electrical load of a magnetic resonance sensor. In the same way, variability in the electrical conductivity of the slurry fluid phase can affect the stability of the electrical load. In the absence of electrical load control, the electrical load variation leads to an imperfect tuning-matching condition and reduces the radio frequency power transfer to and from the sensor. Variation of the electrical load may also lead to variations in the transfer function between sensor and receiver. The result is a loss of sensitivity and incorrect prediction of mineral concentration.
Other examples of on-line slurry analysers include X-ray fluorescence (XRF) analysers for the measurement of elemental concentration and on-line X-ray diffraction (XRD) analysers for the measurement of mineral phases. However such analysers may have some limitation for use in process control. For example, XRF analysis may not be able to be used to infer mineral phase concentration, while XRD analysis may suffer from inadequate detection limits in some circumstances. It would therefore be of benefit to the mineral processing industry if improved sensors and/or apparatus compatible with on-line slurry measurement could be developed.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.